1. Technical Field
The present invention relates generally to a semiconductor device and its method of manufacture. More particularly, the present invention relates to a semiconductor device which features copper metallurgy formed on an amorphous metallic glass barrier layer, and to its method of manufacture.
2. Related Art
To provide higher speed of semiconductor devices, it has become necessary in the art to employ conductive materials of low resistivity and insulators having low-k, i.e., a dielectric constant less than about 4. For example, copper is now becoming the conductive material of choice because of its lower resistivity and better electromigration resistance as compared with aluminum. In addition, as alternatives to silicon dioxide or doped silicon dioxide, such as BPSG, which have dielectric constants above 4, insulation materials with low dielectric constant (k less than 4) have been investigated. For example, in U.S. Pat. No. 5,563,105, a fluorine doped silicon glass (FSG), with a dielectric constant of 3.5-3.7, is described. Also, organic materials having an even lower dielectric constant, such as about 2.7, have been developed for use as insulators. See, for example, U.S. Pat. No. 5,965,679.
For copper metallurgy, the damascene process is typically used, where copper is deposited over the entire patterned insulator surfaces to fill openings, i.e., trenches and vias, followed by planarization, e.g. using chemical mechanical polishing. When the deposition is by electroplating, a plating base or seed layer precedes the deposition, as well as other layers, such as refractory metals or refractory metal nitrides, to improve adhesion and to prevent copper diffusion into the insulator. Because the thickness of such barrier layers needs to be reduced to meet microprocessing requirements, diffusion of copper through the barrier layers into low-k insulators becomes a problem.
In particular, for temperatures for back end of the line processing, i.e., less than 450xc2x0 C., thermal diffusion of copper into oxide or organic insulators is not significant. However, in the presence of an electric field and moisture, copper atoms can be chemically ionized first at the anode, then positive copper ions can migrate rapidly through low-k insulators (so-called electrochemical migration) to the cathode causing reliability problems. Further, outgassing of benzene from organic insulators, such as those described in U.S. Pat. No. 5,965,679, at high temperature can electrostatically attract positive copper ions. Due to the poly-crystalline nature of conventional barrier layers, such layers always have some crystralline defects such as lattice defects, grain boundary, and segregation. Those defects, particularly grain boundary, could serve as a fast diffusion path for copper electrochemical migration. Copper diffusion through conventional barrier layers into low-k insulators can result in increased electronic leakage, increased dielectric constant and premature time-dependent dielectric fail.
Therefore, there exists a need in the industry for an improved barrier layer for copper damascene structures having low-k insulators, and an accompaning method of making such structures.
It is against this background, that the present invention introduces a barrier layer which comprises an amorphous metallic glass for use with copper conductive layers and low-k organic insulators. In general, the barrier layer serves as the primary barrier for preventing diffusion of copper into the low-k organic insulator. In addition, in use, the barrier layer is relatively thin, which allows the low resistivity characteristics of copper to be beneficially utilized in back end of the line metallurgy. The amorphous nature of the barrier layer also provides for adequate formation of a continuous and highly textured copper seed layer, when the copper is deposited in an opening by electroplating, as well as satisfactory adhesion of the copper to the low-k organic insulator.
In accordance with the invention, there is provided a semiconductor device comprising a conductive layer in an opening in an insulator, wherein the conductive layer comprises copper and the insulator comprises a low-k organic material, and further wherein the conductive layer is formed on a barrier layer which comprises an amorphous metallic glass.
Further, in accordance with the invention, there is provided a semiconductor device comprising a conductive layer in an opening in an insulator; wherein the conductive layer comprises copper; wherein the insulator comprises an oligomer, uncured polymer or cured polymer comprising the reaction product of one or more polyfunctional compounds containing two or more cyclopentadienone groups and at least one polyfunctional compound containing two or more aromatic acetylene groups wherein at least one of the polyfunctional compounds contain three or more groups selected from the group consisting of acetylene groups and cyclopentadienone groups; and a barrier layer disposed between the conductive layer and the insulator, the barrier layer comprising amorphous tantalum-aluminum, which contains about 69% to about 75% tantalum. The amorphous tantalum-aluminum alloys have ideal barrier characteristics such as structural homogeneity and the absence of crystalline defects. Their physical and electrical properties can also be adjusted by changing process conditions and compositions.
Additionally, in accordance with the invention, there is provided a method of making a semiconductor device, comprising the steps of forming an opening in an insulator which comprises a low-k organic material; forming in the opening a barrier layer which comprises an amorphous metallic glass; and forming on the barrier layer a conductive layer which comprises copper.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of embodiments of the invention.